Grandmother of All Sauropods Unearthed

Below:

Next story in Science

The first complete skeleton of an early sauropod has been found
in China, providing a glimpse of the ancestor of all those
colossal, four-legged dinosaurs that came later.

The sauropod, tentatively named Yizhousaurus sunae, lived
200 million years ago on the plains of what is today the Yunnan
Province of southern China. Yizhousaurus was 30 feet long
and already had the signature sauropod long neck, heavy-duty
skeleton and four-legged stance.

But what really makes the case for its pivotal role in the
evolution of sauropods is its intact skull, which is an extremely
rare find, explained paleontologist Sankar Chatterjee of Texas
Tech University.

"The skull has very, very crucial information about its
affinities," Chatterjee said. In the case of Yizhousaurus,
the skull is wide, domed, short-snouted and has eye sockets on
the sides to make it easier to watch for predators. It also has a
broad, U-shaped jaw that looks a lot like those seen in later
sauropods.

The teeth tell a lot about the beast as well. Yizhousaurus
had a lot of serrated and spoon-shaped teeth on upper and lower
jaws. These could slice past each other like scissor blades,
allowing Yizhousaurus to shear off the vegetation on which
it dined as well as chew. It also appears that the animal could
raise its head and snip leaves and branches from trees.

The reason few early sauropod skulls are found is that they are
very delicately built compared to the rest of a sauropod,
Chatterjee said. They are also very small despite the huge bodies
they once commanded.

What also helps make the case for Yizhousaurus as a
missing sauropod link are the other fossils near which it was
found. Decades ago fine specimens of what are called prosauropods
were found in the same rocks. As the name implies, prosauropods
are generally thought to be the precursors of the sauropods.

Despite the findings, the transition between them has been fuzzy.
Yizhousaurus helps to sharpen the image a bit.

"I would say this is a very important fossil that will shed light
on the early evolution of sauropodomorph dinosaurs," said Spencer
Lucas, curator of geology and paleontology at the New Mexico
Museum of Natural History and Science. "It once again
demonstrates the richness and importance of the Chinese
vertebrate fossil record."

Chatterjee will be presenting Yizhousaurus discovery on
Oct. 31 at the annual meeting of the Geological Society of
America in Denver.